1. Month Year
doc.: IEEE yy/xxxxr0
September 2010
Update of Interference Management Using Beamforming Technique in OBSS Environment
Authors:
Yusuke Asai (NTT)
John Doe, Some Company

2. September 2010
Abstract
This submission shows the update topics for the interference management technique in OBSSs environment [1][2].
Frame sequence and contents of control / management frames
Security class change
Throughput evaluation
Yusuke Asai (NTT)

3. September 2010
Overview of interference management using beamforming in OBSS environment
Some degrees of freedom on antennas at an AP can be used to mitigate interference to the STAs associated with other BSSs to form null to them.
When two APs mutually form null beams to the STAs associating to the partner’s AP, spatial multiplexing transmission between APs is possible.
AP1
AP2
STA1
STA2
Null beams to the STA on the other BSS
Yusuke Asai (NTT)

4. September 2010
Merits and requirements of the proposed interference management technique
Merits:
Simple implementation: Null-beams can be easily configured because each AP supporting MU-MIMO inherently has a transmit beamforming function.
Throughput improvementMore than 50% throughput improvement is achived.
Smaller latency: Frequency to access medium for AP will increase, which makes QoS data transmission more reliable.
Requirements:
Frame sequence: to form beamforming weight and preparation for spatial multiplexing transmission
Control frame should be extended to call APs / STAs and exchange information between APs.
Yusuke Asai (NTT)

5. Update Points
September 2010
Frame sequence and contents of control / management frames
New type of control frame to initiate the sequence of spatially multiplexing transmission between APs is proposed.
Required actions for APs and STAs on the sequence is also updated.
Security class
We propose that security class of CSI feedback frame is changed 3 to 1.
Brief throughput evaluation including channel life time
When CSI reuse is used, throughput gain reaches up to 50%.
Yusuke Asai (NTT)

6. Frame Sequence for Spatial Multiplexing Transmission between APs
September 2010
Frame Sequence for Spatial Multiplexing Transmission between APs
The frame sequence for the spatially multiplexing transmission between APs comprises three phases:
Initiation phase
Initiator AP calls the responder AP and STAs on its BSS.
Responder AP responds to the initiator AP and calls STAs on its BSS.
CSI feedback phase
Either implicit or explicit feedback is used.
If CSI has been already exchanged, this phase may be skipped.
DATA transmission phase
Spatial multiplexing transmission between APs and Block ACK transmission
Prior to “b. CSI feedback phase” and “c. DATA transmission phase,” “a. Initiation phase is run to establish the frame sequence.
Yusuke Asai (NTT)

7. a. Initiation phase September 2010
When an AP obtains a chance to access medium, the AP can start the sequence for spatial multiplexing transmission between APs.
AP1 (initiator) transmits a CTS-to-Self frame to set the NAV to all STAs associated in AP1.
AP1 transmits an OBSS Control frame (newly defined )to call AP2 (responder) and the destination STAs.
AP2 (responder) transmits a CTS-to-Self frame to set the NAV to all STAs associated in AP2.
AP2 transmits an OBSS Control frame to respond to AP1’s call and to call it’s destination STAs.
AP1
(initiator) CS OC CS
: CTS-to-Self frame
: OBSS control frame
: Null Data Packet
: Block ACK frame 1. 2. OC
STA1
NDP
AP2
(responder) CS OC 3. 4. BA
time
STA2 a.
Yusuke Asai (NTT)

8. OBSS Control Frame September 2010
An OBSS control frame informs parameters of the spatial multiplexing transmission between APs.
APs and STAs synchronize frame timing from the OBSS control frame.
An OBSS Control frame carries the following information:
For the responder AP:
MAC address of the responder AP
The number of available SS (spatial streams) for responder AP’s transmission
The number of spatial streams which the responder AP must form NULLs
For the initiator AP:
MAC address of the initiator AP
The number of
For the STAs associated to AP1
Group ID corresponding to the STAs group
The numbers of spatial streams for STAs
The need of CTS-to-self protection for CSI feedback by STAs
For the all of receivers
Type of the frame sequence
Yusuke Asai (NTT)

9. An example of frame format for OBSS Control (1/2)
September 2010
Octet: 2 2 6 6 6
Frame
Control
Duration
Receiver Address 1
MAC address for Tx AP
MAC address for Rx AP 1 1 2 1 1 4
(continued)
Initiation / Response
Group ID
# of SSs for STAs
# of available SSs for Tx AP
CTS protection
FCS
Frame Control
Type/Subtype： (01) Control frame / (0110) OBSS Control
Duration
Length of duration depends on the pattern of the following sequence.
Receiver Address 1
Group address (assigned for this frame)
STAs and APs that support the spatial multiplexing transmission between APs shall recognize the content of the frame.
MAC address for Tx / Rx AP
(Tx AP, Rx AP) = (initiator AP, responder AP) or (responder AP, initiator AP)
Yusuke Asai (NTT)

10. An example of frame format for OBSS Control (2/2)
September 2010
Octet: 2 2 6 6 6
Frame
Control
Duration
Receiver Address 1
MAC address for Tx AP
MAC address for Rx AP 1 1 2 1 1 4
(continued)
Initiation / Response
Group ID
# of SSs for STAs
# of available SSs for Tx AP
CTS protection
FCS
Initiation / Response
indicates whether this OBSS Control frame is initiation or response message.
Group ID (assigned for this frame)
indicates the Group ID that corresponds a group of STAs in initiator / responder AP to join the spatial multiplexing transmission between APs.
# of SSs for STAs
informs the numbers of spatial streams for STAs in the Group ID.
The Rx AP must form NULL streams as many as summation of “# of SSs for STAs.”
# of available SSs for Tx AP
The number of spatial streams that Tx AP can handle.
(the maximum # of SSs for Rx AP’s STAs) = (the # of available SSs for Tx AP) – (summation of “# of SSs for STAs.”)
CTS protection
Tx AP can order it’s STAs to use protection of CTS-to-Self frames by using this field (bitmap based).
Yusuke Asai (NTT)

11. OBSS Control frame as Control Wrapper frame
September 2010
Octet: 2 2 6 2 4 18 4
Frame
Control
Duration
Receiver Address 1
Carried Frame Control
HTC
Carried Frame
FCS
When CSI feedback sequence between APs, OBSS Control frame as Control Wrapper frame is used.
Frame Control
Type/Subtype： Control frame/Control Wrapper
Duration
Length of duration depends on the existence of CSI feedback (implicit/explicit), CTS frames from STAs and DATA transmission.
Receiver Address 1
Group address
Carried Frame Control
Subtype: 0110 (OBSS Control frame)
HTC field
Specify the type of CSI feedback scheme (implicit or explicit or “no use”.)
Carried frame
is identical to OBSS Control frame without “Frame Control,” “Duration,” “Receiver Address 1.”
Yusuke Asai (NTT)

12. Sequence Types (1/4) September 2010
DATA transmission only (“a. Initiation” + “c. Data transmission”)
OBSS Control frame is not Control Wrapper.
This sequence can be used only when transmit beam for spatial multiplexing transmission between APs is prepared on each AP prior to the sequence.
AP1
(initiator) CS OC
Data for STA1 BA
STA1
AP2
(responder) CS OC
Data for STA2 BA
time
STA2 a. c.
(by CS from AP1)
(by OC from AP1)
NAV
settings
(by CS from AP2)
(by OC from AP2)
Yusuke Asai (NTT)

13. Sequence Types (2/4) September 2010
Implicit feedback only (“a. Initiation” + “b. CSI feedback”)
AP1
(initiator) CS OC
The OBSS Control frames are Control Wrapper frames and HTC field is set to implicit feedback.
NDP
STA1
AP2
(responder) OC MR
NDP
time
STA2 a. b.
(by CS from AP1)
(by OC from AP1)
NAV
settings
(by CS from AP2)
(by OC from AP2)
Yusuke Asai (NTT)

14. Sequence Types (3/4) September 2010
Implicit feedback + DATA transmission
The 1st OCs are Control Wrapper frames
The 2nd OC are not Control Wrapper frames.
AP1
(initiator) CS OC CS OC
Data for STA1
NDP BA
STA1
AP2
(responder) CS OC CS OC
Data for STA2
NDP BA
time
STA2 a. b. c.
(by the 1st CS from AP1)
(by 2nd CS from AP1)
NAV
settings
(by 2nd OC from AP1)
(by 2nd CS from AP2)
(by the 1st
OC from AP1)
(by 2nd OC from AP2)
(by 1st OC from AP2)
(by 1st CS from AP2)
Yusuke Asai (NTT)

15. Sequence Types (4/4) September 2010 Explicit feedback only
Implicit feedback + DATA transmission
AP1
(initiator) CS OC
NDP
CSI FB
CSI FB
STA1
The OBSS Control frames are Control Wrapper frames and HTC field is set to explicit feedback.
AP2
(responder) CS OC
NDP
CSI FB
CSI FB
time
STA2 a. b.
AP1
(initiator) CS OC
NDP CS OC
Data for STA1
time
CSI FB
CSI FB BA
STA1
AP2
(responder) CS OC
NDP CS OC
Data for STA2
CSI FB
CSI FB BA
STA2 a. b. c.
Yusuke Asai (NTT)

16. CTS protection September 2010
Initiator/responder AP can request STAs to transmit additional CTS-to-self frame prior to their transmission.
AP1
(initiator) CS OC CS OC
Data for STA1
STA1
(w/ CTS) CS
NDP CS BA
AP2
(responder) CS OC CS OC
Data for STA2
NDP BA
time
STA2 a. b. c.
(by 1st CS from AP1)
(by 2nd CS from AP1)
(by 1st OC from AP1)
(by 2nd OC from AP1)
NAV
settings
(by 2nd CS from AP2)
(by 1st CS
from AP2)
(by 2nd OC from AP2)
(by OC from AP2)
(by 2nd CS from STA1)
(by 1st OC from STA1)
Yusuke Asai (NTT)

17. Security Class Change September 2010 b. a. c. a. c.
Three types of connections are used for the proposed sequences.
The connections between an AP and an STAs within a BSS: State 3 (Authenticated, Associated )
CTS-to-Self frame (Class 1)
OBSS Control frame (control frame: Class 1)
NDP (just a preamble signal)
DATA frame (Class 3)
BlockACK frame (Class 3)
The connections between initiator and responder APs: State 1 (Unauthenticated, Unassociated)
CTS-to-Self frames (Class 1)
OBSS Control frames (Class 1)
The connections between an AP and an STA associated to the other AP: State 1
CSI feedback frames (management frame: Class 3)
(defined as no “Robust” management frame in )
Figure Relationship between state variables and services
AP1
AP2 b. a. c. a. c.
STA1
STA2
To establish CSI feedback connection between an AP and an STA associated to the Other AP, it is proposed that the class of CSI feedback frames is changed from Class 3 to Class 1.
(This change does not degrade security level specified in 11w.)
Yusuke Asai (NTT)

18. Throughput Evaluation
September 2010
Throughput Evaluation
Evaluation Parameters
Parameter
Value
# of APs 2
# of Tx/Rx antennas per AP 8
# of Tx/Rx antennas per STA
# of STAs per AP
1 / 2 / 3 / 4
# of subcarrier per spatial stream
234
Frequency bandwidth
80 MHz
MCS
64QAM, R=5/6
MSDU size
1500 Byte
A-MPDU size
64kByte
Yusuke Asai (NTT)

19. Frame sequence without interference management (implicit feedback)
September 2010
Frame sequence without interference management (implicit feedback)
One user per AP case, an AP transmits SU-MIMO frames.
(SU-MIMO without CSI feedback is assumed
Data for STA1
(medium busy)
AP1
(SU-MIMO) BA
(medium busy)
STA1
(medium busy)
Data for STA2
AP2
(SU-MIMO)
(medium busy) BA
STA2
Data transmission
from AP1 to STA1
Data transmission
from AP2 to STA2
(Channel access phase based on DCF)
Yusuke Asai (NTT)

20. Frame sequence without interference management (implicit feedback)
September 2010
Frame sequence without interference management (implicit feedback)
Two users per AP case, an AP transmits DL MU-MIMO frames.
HTC+
Data for STA1/2
(medium busy)
AP1
(DL MU-MIMO)
NDP BA
(medium busy)
STA1
NDP BA
STA2
(medium busy)
(medium busy)
HTC+
Data for STA3/4
AP2
(DL MU-MIMO)
(medium busy)
NDP BA
STA3
NDP BA
(medium busy)
STA4
Data transmission from AP1
to STAs1 and 2
Data transmission from AP2
to STAs3 and 4
(Channel access phase based on DCF)
Yusuke Asai (NTT)

21. Throughput Evaluation
September 2010
Throughput Evaluation
Implicit feedback and CSI feedback per 10ms are assumeded.
Through improvement reaches 48% when the number of STAs per AP is 2 by spatial multiplexing transmission between twp APs.
It can saturate throughput even when traffic per AP is not saturated.
48%
Normalized throughput
The number of STAs per AP
Yusuke Asai (NTT)

22. Throughput Improvement as a function of CSI lifetime
September 2010
Throughput Improvement as a function of CSI lifetime
40-58% improvement
Throughput improvement depends on the length of CSI lifetime.
When CSI lifetime is longer, less frequent CSI feedback is required.
40-58% throughput performance improvement can be achieved by the proposed scheme.
Normalized Throughput Improvement
The number of STAs per AP
Yusuke Asai (NTT)

23. September 2010
Summary
This submission shows the update points for the interference management technique in OBSS environment in terms of following topics:
Frame sequence and contents of control / management frames
Security class change
Throughput evaluation
Throughput evaluation shows that the proposed interference management using transmit beamforming improves throughput performance in OBSS environment by up to 58%.
Yusuke Asai (NTT)

24. September 2010
References
[1] Yusuke Asai, “Interference Management Using Beamforming Technique in OBSS Environment,” Doc. IEEE /0585r4. [2] Yusuke Asai, “Frame Sequence of Interference Management Using Beamforming Technique in OBSS Environment,” Doc. IEEE /0831r0.
Yusuke Asai (NTT)